Fun with a boroscope - II: installing structural foam in the front subframe cavity

[mscott7426]

Foam does not fix the fundamental problem. Its a band aid for some of the symptoms. The core problem is that the rear of the RACP is not directly attached to the chassis rails but instead goes under the rails into a single sheet and attaches to the wheel arches. This poor design inherently flexes and putting some goo around the rear gussets is not gonna stop that.

The only permanent solution is to attach the RACP directly to the chassis rails so it cant flex anywhere near as much (e.g.: using CMP rail plates or Vincebar) - and foam will make that more difficult to do.

Do the cross bar fixes stop the spread of damage of the front mounts? My front right mount has far more damage than the others.

[poss]

Do the cross bar fixes stop the spread of damage of the front mounts? My front right mount has far more damage than the others.

The way I understand the engineering issue from info on sites like CMP is that acceleration cycles force the rear left mount to flex up/down - which in turn causes the opposite front right mount to do the converse - eventually causing metal fatigue stress fractures around the mounting gusset spot welds, and then the damage will continue to spread further. Failures most commonly show up first in the rear left and front right subframe mounts because of this rotational flexing, and its also why M3's exhibit the problem worse than other E46's (more power - more flexing and thus quicker fatigue)

A vincebar, CMP bar, or even just the CMP rail plates without a bar will significantly reduce if not eliminate the ability for the rear left mount to flex cos now its directly attached to the chassis rail (as BMW should have done in the first place!) rather than by a 'trampoline' of sheet metal. The CMP rail plates are the cheapest solution, but personally I'd put in a bar as well while you're there unless your budget is really tight.

By reducing/eliminating the flexing of the rear left mount it will have a corresponding effect on the front right mount - but there will still be rotational forces in play and I believe another problem with the front mounts is caused by the metal in the bushings indenting into the sheet metal - which isn't thick enough to stop this.

Proper topside reinforcement will slow down further damage to the front mounts but probably wont stop it completely. If you already have damage to the mounts then you need to fix this anyway by welding the cracks and installing underside plates

[mscott7426]

K thanks. I have plates to be installed, but after subframe removal I noticed the cracking on the front right mount. Originally I was going to epoxy the plates, and do the foam, but since I need to weld the cracks to repair, I'm wondering what other longer term solutions I should consider.

I drilled some holes like Redish describes in their videos and found some cracking around the tops of the front mounts so I was more wondering if bottom plates and a top support for the rear mounts (like SME bar or CMP plates) would mitigate this.

Edit: Sorry for the thread hijack martin, I can start a new one if you'd like.

[poss]

K thanks. I have plates to be installed, but after subframe removal I noticed the cracking on the front right mount. Originally I was going to epoxy the plates, and do the foam, but since I need to weld the cracks to repair, I'm wondering what other longer term solutions I should consider.

I drilled some holes like Redish describes in their videos and found some cracking around the tops of the front mounts so I was more wondering if bottom plates and a top support for the rear mounts (like SME bar or CMP plates) would mitigate this.

Edit: Sorry for the thread hijack martin, I can start a new one if you'd like.

You can start another thread if you like - but yes, since you need to weld anyway you might as well go the whole hog. If you fix the existing damage then plates and top rear reinforcement should provide a permanent fix I prefer the Vincebar style solution because its invisible (doesn't protrude into boot space) and pretty easy to manufacture yourself if needs be out of 20mm square bar and 3mm plate. Aside from obtrusiveness I am not a big fan of X-style braces as an RACP solution. IMHO bolting a brace to the turrets cannot offer the same effectiveness as connecting the rear mounts directly to the chassis rails via a substantial square section steel bar (tho perhaps a brace is worth considering as an easier alternative if there's no pre-existing cracking)

The aim is to eliminate any up/down flexing. X-style braces introduce several potential weak points where this could still occur - tho still superior to foam around the gussets, which will have little effect other than to delay the inevitable (others have suggested that BMW's use of foam was likely just the cheapest way they could get vehicles that hadn't cracked yet through the warranty period)

[old///MFanatic]

others have suggested that BMW's use of foam was likely just the cheapest way they could get vehicles that hadn't cracked yet through the warranty period

1) What warranty time period are you suggesting this corresponded with?
2) When are you saying BMW was using epoxy foam on non-cracked RACP?

[poss]

1) What warranty time period are you suggesting this corresponded with?
2) When are you saying BMW was using epoxy foam on non-cracked RACP?

I believe BMW extended the RACP warranty to 10 years in the US after settling the Sub-frame Defect Class Action Lawsuit

As no-one else outside of the US bothered to sue BMW it was the standard chassis warranty time period for that country (usually 3-5 years) - although here in Australia I understand a chassis must last for 10 years in order to meet statutory compliance (otherwise the entire model is unfit for sale).

My indy is a former BMW master mechanic who directly dealt with the M3 RACP cracking issue occurring on cars still under warranty. The authorised BMW fix here in Australia (and elsewhere I assume) was:

• If the crack length was less than 11mm then just pump foam into cavity around the gussets, otherwise
• Take out and weld in a new RACP

So yes, correction. BMW used foam when there was only minor cracking. If there is no visible sign of damage then BMW isn't going to effectively admit there's an issue by doing preventative structural maintenance.

[old///MFanatic]

I believe BMW extended the RACP warranty to 10 years in the US after settling the Sub-frame Defect Class Action Lawsuit
authorised BMW fix here in Australia (and elsewhere I assume) was:

• If the crack length was less than 11mm then just pump foam into cavity around the gussets, otherwise
• Take out and weld in a new RACP

So yes, correction. BMW used foam when there was only minor cracking. If there is no visible sign of damage then BMW isn't going to...

1) No BMW did NOT extend the warranty to 10 years.
2) 20mm not 11mm and it depends on the build date.

Yes statement about BMW using the structural epoxy was wrong to get cars through some warranty. Just good to have the correct info out on forum is all. So guess we can let these "others" you mentioned who suggest this, that it is incorrect and doesn't hold water.

[poss]

Originally posted by oldFanatic

Yes statement about BMW using the structural epoxy was wrong to get cars through some warranty.

oldFanatic, that's a baseless claim. You provide no evidence (apart from attacking me - which is not evidence).

It is self-apparent that the RACP cracking is due to metal fatigue.

By your lack of bluster on the point you appear to concede that BMW did indeed repair vehicles entirely differently based on the crack length - 11mm or 22mm matters not. It's a goddamn metal fatigue-induced stress crack and it's simply gonna get worse unless you stop the fundamental cause of the metal fatigue.

Do you think BMW didn't recognise the cause was metal fatigue? - of course they did (they're not idiots) - and it's safe to assume their bean counters recognised the difference in cost between pumping some foam gunk into a hole and having to perform major surgery (the RACP replacement costs $11,000 here and it still doesn't fix the root cause. The new panel will simply fail sooner or later like the original did - just as the 11mm or 22mm crack will grow larger and the damage spread to other areas. Foam is not a permanent fix to the structural design flaw. It merely slows down the spread of cracking)

I believe BMW offered a 10 year window for repairs or reimbursement as part of the US 'subframe' class action settlement. If you want to quibble that's not a warranty then fine. Who cares!

BTW: Here's the press announcement from BMW concerning the US settlement. AFAIAK it is complete horseshit for BMW to purport the cracking happens only under "rare conditions". Note they stress it's not a recall of any kind, and that the offer only applies to owners in the US. It is obvious to me that all BMW was doing here is covering their own financial arse :

""BMW has agreed to a proposed settlement of a class action lawsuit concerning the Sub-Frame structures on 3 Series ("E46") models produced from 1999 through 2006. Under rare conditions the attachment points of the Sub-Frame may develop a fracture or crack. BMW has prepared an inspection, approved repair procedure, and reimbursement policy in keeping with the terms of the proposed class settlement. This settlement will only pertain to US residents and is not a recall of any kind. Details will be forthcoming, pending the court's final approval of the proposed class settlement."

[old///MFanatic]

Pardon me but I’m not sure what you’re going off about. Sorry you’ve taken offense, but you’re stating things incorrectly and I’m simply just giving correct info you state “others” say. No biggie, try keep things friendly and to the point.

Sorry but it’s not baseless, it is correct.
1) BMW did not extended warranty 10 years. If that were the case a 2006 M3 would be covered until 2016. We know this is not the case.
2) BMW did not add foam structural epoxy just to get cars cheapest through the warranty period. Warranty was well over for almost all of these. Some cars under warranty had fixes vary depending on extent of damage and build date.
3) BMW did not add foam structural epoxy to cars that did not have cracks yet. Hundreds of thousands of E46s did not have damage in their lifetime.
4) 20mm is the correct spec BMW used. Not baseless, it’s direct from BMW documents.

An internet search even prior to BMW’s US voluntary inspection settlement will find me providing info on it on the forums. I would even get requests from BMW dealerships for the internal documents they said they could not get. I’m more than a little familiar with it.